Legacy-BIOS

In order to turn off UEFI booting you will need to boot into your BIOS and change the boot mode to Legacy. Afterward, follow the Beginner's Guide for standard installation instructions.

UEFI

Installation from UEFI bootable USB works with the default bootloader, so rEFInd is unnecessary. In the BIOS under Startup, set "UEFI/Legacy Boot" to UEFI only.
The default partition table (and Windows installation) uses MBR. For UEFI, reformat the disk as GPT.

Booting using an efibootmgr entry works well. The warnings about incompatibility and embedding arguments to do not apply.

Hardware

Almost everything works out of the box. Install synaptics and video-intel drivers.

Fingerprint Reader

fingerprint-gui from the AUR is already patched to work with the X1's newer fingerprint reader. To get the gui's dropdown to recognize your device, you'll have to add your user to the plugdev group:

# gpasswd -a <username> plugdev

It has been seen that the relevant udev rules do not get set properly. To do this, open /usr/lib/udev/rules.d/40-libbsapi.rules with your favorite text editor to add (or create with) the following lines: